It is desirable for devices, such as mobile devices, to have the ability to both quickly resume operations from a hibernation state (also known as an idle mode) and to store data for extended periods of time in a hibernation state while consuming small amounts of power. Typically mobile devices include a controller device and a non-volatile storage device. The controller device is comprised of a processing unit and a high performance volatile RAM memory. The storage device may include a flash memory array, (e.g. NAND array), which is a long term non-volatile memory, and a number of buffers and associated circuitry. When the system is awake the buffer will typically be used as an intermediate memory between the controller and the flash array. In programming mode, the buffer will receive data from the controller and the data stored in the buffer will be used to program the flash array. When reading from the flash, a sensing operation will be applied to the flash array, and the results of the sensing will be processed by the associated circuitry and stored in the buffer. The contents of the buffer will then be transferred to the controller for further processing (e.g. ECC decoding). Two options are commonly considered for hibernation. Long period hibernation is typically preceded by copying data from the volatile memories (e.g. the controller RAM) into the non-volatile memory, and shutting the power from the volatile RAM. Short period hibernation may be implemented by reducing the power consumption of the volatile RAM to a minimal level required for maintaining the data. Both methods have their advantages and disadvantages. Shutting down all the volatile memory has the ability to withstand long hibernation periods, but results in a long wake up period, when the mobile device becomes active again. Reducing the power to the RAM enjoys a fast wake up time but the RAM continues to draw power from the device, and therefore it may be used for a limited time only.
Improved hibernation methods are desirable for use in devices such as mobile devices that are able to provide the speed of memory such as with DRAM memory, while providing the ability to store data for extended periods of time while consuming small amounts of power such as with NAND memory.